Remove use of deprecated logging methods.

[Julian]

Logger.warn is spelled Logger.warning.

[PatrickMassot]

Do you have references about this deprecation? Which python versions use the new spelling?

[Julian]

Sorry, I was lazy -- logger.warn was deprecated for 10 years or so at least, it's from before the module was incorporated into the standard library:

⊙  python3 -W default -c 'import logging; logging.getLogger().warn("Hello")'                                                                                                        julian@Airm
<string>:1: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
Hello

See e.g. https://bugs.python.org/issue13235 -- which looks like it says it was deprecated at least back since 3.3.

[PatrickMassot]

Thanks